Thomas Frank criticised referee Simon Hooper for not sending off Will Vaulks during Brentford’s 2-2 draw at Cardiff.
The Bluebirds midfielder appeared to knee Christian Norgaard in the head but the incident went unpunished.
Brentford were two up at the time after goals from Luka Racic and Bryan Mbeumo.
Having stayed on the pitch, Vaulks was then involved in goals by Junior Hoilett and Joe Ralls as Cardiff secured a point and extended the Bees’ winless run to five matches.
Frank revealed: “I said to Vaulks after the game: ‘You are a very good player and I know you are not a player like that’ – because he is not a dirty player.
“But this one was a red card. The fourth official, linesman – too soft. They saw it, 100%.”
The result left fifth-placed Brentford 11 points behind second-placed Leeds.
“I was pleased with the attitude of my players coming to Cariff, which we know is a tough place to come to,” Frank added.
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